1. Field of the Invention
The present invention relates to a line width measuring method for measuring the line width of a pattern formed in a resist film on a substrate, a substrate processing method, a substrate processing apparatus, and a substrate cooling processing unit.
2. Description of the Related Art
In a photolithography step in a manufacturing process of a semiconductor device, a predetermined pattern is formed in a resist film on a wafer by sequentially performing a plurality of treatments and processing, for example, a resist coating treatment to form the resist film by applying a resist solution onto the wafer surface, exposure processing to expose the wafer to light by applying light through the predetermined pattern onto the resist film on the wafer, a developing treatment to selectively dissolve the exposed resist film by a developing solution, and so on.
After the pattern is formed on the wafer, line width measurement of measuring the line width of the pattern is performed to check whether the pattern is properly formed.
For the line width measurement, an optical line width measuring method of measuring the line width using light is used in recent years. The optical line width measuring method is excellent in that it can restrain shrinkage of the pattern on the wafer because electrons never strike against the wafer, unlike an electron line width measuring method conventionally performed.
The above-described optical line width measurement is performed using the so-called scatterometry technique (Japanese Patent Laid-open No. 2002-260994 and Japanese Patent Laid-open No. 2003-209093).
The scatterometry technique means that calculation is performed to obtain a plurality of calculated light intensity distributions for a pattern in an arbitrary shape to create their library in advance, so that at the time of measurement of the line width, light is applied onto a real pattern that is an object to be measured and the intensity distribution of reflected light reflected from the pattern is measured, and the measurement result is matched to the calculated light intensity distributions in the library, whereby the line width of the pattern in the library having a matching light intensity is estimated to be the line width of the real pattern on the wafer.
In the above-described scatterometry technique, to calculate the light intensity distributions for an arbitrary pattern and create their library, optical constants such as a refractive index, an extinction coefficient, and so on of the resist film that is the material of the wafer surface are required. Therefore, in the conventional optical line width measurement, a standard refractive index and extinction coefficient of a resist material, for example, provided from a material manufacturer or the like have been used to calculate the light intensity distribution for an arbitrary pattern.
However, when the resist material is actually applied onto the wafer and a plurality of treatments and processing are performed on the wafer, the property of the resist film on the wafer to light changes. In addition, the change also differs among wafers due to slight variations in processing states. Accordingly, the optical constants of the resist film onto which light is applied when the line width is actually measured differ from those before the processing and also differ among wafers. Therefore, the light intensity distributions in the library are calculated based on values different from the optical constants of the resist film at the time of actual measurement, and accordingly the line width of the pattern decided through matching to the light intensity distributions in the library is far from accurate.
Unless the line width of the pattern is accurately measured, even if there occurs a case in which the line width of an actually formed pattern is not proper, that case cannot be detected. This may lead to manufacture of a large amount of defective wafers. Especially, in recent years, very fine pattern shapes are demanded, and defective wafers cannot be detected without more accurate line width measurement.